Heating oil was stolen from the boiler that heats North Somercotes Primary School’s outdoor swimming pool.
Around 500 litres of oil was taken sometime on the night of Tuesday July 9.
Headteacher Paul Floyd said to ensure pupils could continue to swim before the end of term the school had to order more oil at a cost of £360.
Youngsters at North Somercotes Playgroup also use the school pool.
Supervisor Julie Sharp said: “We are very lucky that the primary school has an on site pool and that both students and playgroup children can access this pool.
“We are horrified that these people are stealing from the children.”